1. Field of the Invention
The present invention relates to an organic electroluminescence element and the method for manufacturing thereof. In particular, the present invention relates to an organic electroluminescence element and a method for manufacturing thereof in which the transmission of moisture and oxygen is prevented.
2. Description of the Related Art
An organic electroluminescence element is expected to be used for various purposes, for example, a flat panel display such as a TV, a computer monitor or a mobile device and an illumination device.
An organic electroluminescence element is a self-luminous element, which is different from a liquid crystal display or the like. An organic electroluminescence element has the following merits. A structure can be extremely thin and a display image can be seen in a large field of view. Moreover, a response speed of an organic electroluminescence element display image is fast and power consumption is low. In addition, a contrast of an organic electroluminescence element is high. Therefore, because of the above merits, an organic electroluminescence element is expected as a flat panel display which takes the place of a cathode-ray tube display and a liquid-crystal display.
FIG. 4 is a schematic cross-sectional diagram of a hitherto known organic electroluminescence element 40. As shown in FIG. 4, a hitherto known organic electroluminescence element 40 has a first electrode 42 and a second electrode 44 on a glass substrate or a plastic substrate 41 and has a structure in which an organic luminescent medium layer 43 is between the two electrodes. At this time, at least one electrode has translucency. An organic electroluminescence element is a self-luminous element for a display in which an organic luminescent medium layer emits light by applying a voltage between the two electrodes. Moreover, an organic luminescent medium layer 43 includes a hole injection layer, a hole transport layer, an organic luminescent layer, and electron transport layer and an electron injection layer. As an example of the organic luminescent medium layer 43, copper phthalocyanine for a hole injection layer, (3,4-ethylenedioxy thiophene)/polystyrene sulfonic acid (PEDOT/PSS) for a hole transport layer, Tris(8-quinolinol)aluminium for an organic luminescent layer, 2,5-bis(1-naphthyl)-1.3.4-oxadiazole for an electron transport layer and lithium fluoride for an electron injection layer can be exemplified. However, an organic electroluminescence element has a problem in that the organic electroluminescence element is degraded by external oxygen and moisture. Therefore, a following method has been generally used. First, an organic electroluminescence element is protected by a first passivation layer 45 and is sealed by a metal can or a glass cap 47 which includes a desiccant 48 using an adhesive layer 46. Next, an organic electroluminescence element is separated from the air. (See Patent Documents 1 and 2.) Here, the first passivation layer 45 has high barrier properties for oxygen and moisture and is preferred to have insulating characteristics since the first passivation layer 45 is formed on a second electrode (cathode) 44. For example, silicon nitride can be exemplified as the first passivation layer 45. Moreover, as an adhesive layer 46, an epoxy resin can be exemplified. As a desiccant 48, calcium oxide can be exemplified.
However, it is difficult to completely separate an organic electroluminescence element from oxygen and moisture which is degradation factors of an organic electroluminescence element. Therefore, for example, in patent document 3, a technique for eliminating harmful effects for an organic electroluminescence element while a moisture absorbent is fixed by a porous sheet is disclosed. (Patent Document 3)
Moreover, a glass cap is preferably not used in terms of a cost and production of a thin organic electroluminescence element. Therefore, a structure in which a sealing substrate having a flat sheet structure is used is required instead of using a glass cap. However, when a sealing substrate which has a flat sheet structure is used, a desiccant (a moisture absorbent) cannot be contained. Therefore, at this time, it is important to prevent transmission of moisture or oxygen through an adhesive layer itself and the interfacial surface of the adhesive layer and the sealing substrate without the desiccant. However, a degradation of an organic electroluminescence element cannot be prevented in this case, because the adhesive layer and the interfacial surface of the adhesive layer cannot be protected only by a first passivation layer directly formed an organic electroluminescence element.
As mentioned above, in order to obtain a thin organic electroluminescence element, it is important to protect against moisture and oxygen transmitted through the interfacial surface of an adhesive layer and a substrate. However, it is very difficult to protect an organic electroluminescence element sufficiently only by an adhesive layer because an adhesive layer can be peeled from the interracial surface under rapid temperature changes or under high temperature and high humidity environment. Therefore, a barrier layer is preferably formed in order to protect an adhesive layer itself from external atmosphere.
The purpose of the present invention is to provide a thin and light organic electroluminescence element having a long life and a method for manufacturing thereof in which penetration of oxygen and moisture into a sealing edge, in particular, an adhesive layer itself and the interfacial surface of the adhesive layer and a substrate is controlled for the long term.    Patent Document 1: JP-A-H7-169567    Patent Document 2: JP-A-H10-12376    Patent Document 3: JP-A-2001-176655